This invention relates to high voltage arrester devices contained within gas insulated metal enclosures such as described within U.S. Pat. Nos. 3,767,973, 3,842,318 and German Pat. No. 888,132.
When a plurality of zinc oxide type varistor disks are arranged in a stack configuration and electrically connected in series, the capacitive properties of the disks creates the combination of both series capacitance circuits along the stack and parallel capacitance circuits between the individual varistors in the stack and ground. When a high voltage is applied to the line end of the stack, the electric field becomes adversely distorted resulting in a nonuniform distribution of voltage across the stack from the line end to the ground end thereof. A disproportionate share of the applied voltage appearing across the varistors closest to the line end of the stack could cause severe damage to these varistors. This is a particularly severe problem for gas insulated, metal enclosed surge arresters because of the adverse influence of the enhanced capacitance to ground caused by the presence of the metal enclosure.
The purpose of this invention is to provide a means for grading the capacitances occurring along the varistor stack in such a manner as to cause the voltage distribution to become more nearly linear.